For the second time the Apostle John is recorded as having fallen down to worship at the feet of an angel and is rebuked by the angel (Rev. 22:8; 19:10).

How could John commit such a grievous sin? What IS John's problem?

John's problem is one every human being has. "Nothing is more carefully guarded in the Bible than the purity and simplicity of worship; nothing is more sternly rebuked than idolatry; nothing is more contrary to the divine law than rendering in any way that homage to a creature which belongs of right to the Creator. It was necessary to guard even John, the beloved disciple, on that subject; how much more needful, therefore, is it to guard the church at large -- and, I would add, your own heart -- from the dangers to which it is liable." -- Albert Barnes.